Immune cells often infiltrate testicular germ cell neoplasms, including pre-invasive carcinoma in situ (CIS), but the significance of this phenomenon remains unknown. The composition and distribution of infiltrating immune cells were examined by immunohistochemistry in testis samples with CIS and overt seminoma, in comparison to biopsies from infertile men without neoplasia. The composition of immune cells was similar across all the groups studied. Macrophages, CD8(+) and CD45R0(+) T lymphocytes constituted the majority of infiltrates, B lymphocytes were present in an intermediate proportion and very few CD4(+) and FoxP3(+) T cells were detected. HLA-I antigen was more abundant in Sertoli cells in tubules containing CIS than in those with normal spermatogenesis. This study showed a phenotypically comparable composition of infiltrating immune cells independently of the presence of neoplasia, suggesting the absence of active immune surveillance in testicular germ cell cancer.